Hi sil, thanks for your lengthy and detailed reply.
My set up is normally fixed and nothing changes and only recently have I taken it apart to add an OAG... that is another story. I've gone back and used a blower to remove any surface dust that may have found its way onto the optics... filters, camera and front of OTA glass. The imaging sensor is sealed and I couldn't see anything obvious on the glass but that could be my aged eyes playing funny tricks with me
I put everything back together and played around with the setup the other night to get focus on both the imaging camera and guiding camera... it's proved to be a bit of a challenge and still not got it right
On first appearance, images taken, and they were purely for focusing the guide camera, it seems that I have removed whatever was causing the large dust spot. It clouded over quicker than I could set up so not many test shots taken. I haven't attempted to do anything else with the OTA glass at this stage until I am able to get a good night, and all the planets are aligned, for me to be able to get out there and give it another shot... that can be some time away as I am not always feeling up to it when skies do happen to be clear. From what I can see, the glass is in definite need of a proper clean but I'm not sure that I am up to the task. I don't want to risk causing any irrepairable damage to the glass so for now I'll keep doing as in the past.
As for mosaics, I have attached a couple if images of Eta 4x4 mosaic. One is straight out of MaximDl and the other I have only adjusted the levels in Photoshop... very minor. This was taken back in Feb this year when I believe the optics to have been in a better state than now. I know that I have a lot of work to do when it comes to processing as it is not one of my strengths so I am happy with the "trial and error" approach for now and to be honest I don't think that will improve in a great hurry
